Genetic building blocks may have formed in space

The Murchison meteorite contains the building blocks of DNA and RNA, which may have an extraterrestrial origin (Copyright: Chip Clark/Smithsonian Institution/www.si.edu)

Some fundamental building blocks of our genetic code might have come from outer space, according to a controversial new meteorite study.

The study suggests that some organic compounds associated with genetic material might have formed in a meteorite called Murchison before it landed in Australia in 1969. In the mass of organic chemicals isolated, the team found two ring-shaped carbon-containing molecules&colon; uracil, a base that is essential for the creation of RNA, and xanthine, a close chemical relative of the DNA base, guanine.

The find might bolster claims that meteorites delivered some of the chemicals needed to create life. “It boosts the idea that the origin of life on Earth may have had an important contribution from an extraterrestrial object,” says lead author Zita Martins, a chemist at Imperial College London in the UK.

But it may be too early to conclude these nucleobases formed beyond the Earth, says Sandra Pizzarello, a chemist at Arizona State University in Tempe, US. The study “raises a very interesting question that was raised a very long time ago, but I don’t think it solves it”, she told New Scientist.

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No one knows how life got its start. Primitive Earth conditions might not have been favourable for the chemistry needed to create life’s building blocks.

Meteorite impacts

Instead, researchers have argued that frequent bombardments by meteorites 3.8 billion years ago – when life is suspected to have first emerged – could have delivered the material to Earth, where it might have helped further the development of life.

Studies of meteorites, as well as astronomical observations of interstellar dust and gas, have turned up a number of organic compounds, including sugars and phosphates.

But nucleobases are also needed to make a nucleic acid like DNA or RNA. Such chemicals have been found in a number of meteorites, but no one was sure whether they were extraterrestrial in origin or the result of earthly contamination.

Noisy signal

To study the origins of these nucleobases, Martins and colleagues studied the mass of organic chemicals isolated from the meteorite.

The team looked at two different isotopes of carbon in the nucleobases uracil and xanthine. The lighter version, carbon-12, is present on Earth in large amounts. Carbon-13 is more common in sweeping clouds of cold, interstellar gas. Large amounts of the stuff usually indicate the material did not form on Earth.

The ratio of carbon-13 to carbon-12 was unusually high in the two nucleobases, leading the team to conclude the materials likely formed in the meteorite itself rather than on Earth.

But Pizzarello says too many other chemicals were present in the samples to clearly distinguish the carbon ratio. “Analytically, it’s not convincing,” Pizzarello told New Scientist.